1. Field of the Invention
The invention relates in general to elevator systems, and more specifically, to new and improved speed monitoring apparatus for elevator systems.
2. Description of the Prior Art
Speed monitoring and limiting devices adjacent to the terminals or travel limits of an elevator car may monitor the floor selector. If the floor selector is not operating in a manner which will produce a normal slowdown, an auxiliary speed pattern is produced for controlling terminal slowdown. In a prior art arrangement for monitoring an electromechanical floor selector, a long cam is disposed adjacent each terminal. The cam opens a series of switches mounted on the elevator car, one after another, as the car approaches a terminal floor. If the floor selector is operating properly, for each cam operated "switch opening" in the hoistway, there will be a "switch closing" on the floor selector carriage. If this fails to occur, an auxiliary speed pattern is provided.
Speed monitoring and limiting devices adjacent to the terminals may monitor the speed pattern generator as the elevator can approaches a terminal. A terminal slowdown pattern is provided in place of the normal deceleration pattern when a malfunction is detected, to decelerate the car into the terminal floor. Modification of the speed pattern generator signal, however, will not cause the car to decelerate if there is a problem in the drive system. Also, the speed pattern generator may be functioning correctly, but because of a problem in the drive system, the car may not be decelerating along a desired trajectory as it approaches a terminal floor. Such a system takes no action and may allow the car to approach the terminal at an excessive speed.
A speed monitoring system which monitors car speed as a function of car position can provide a high degree of protection against approaching a terminal at an excessive speed. U.S. Pat. No. 3,779,346, which is assigned to the same assignee as the present application, discloses such a system which continuously monitors the car speed as a function of car position, as the car approaches each terminal floor. In this arrangement, closely spaced markers mounted in the hoistway adjacent each terminal cooperate with a sensor disposed on the car to provide a continuous speed error signal which is used in a reference circuit to detect overspeed. The speed error signal is also used in a circuit which generates an auxiliary slowdown pattern. The auxiliary slowdown pattern is substituted for the normal speed pattern when overspeed is detected. If the problem is not in the speed pattern circuits, but in the drive, generation of an auxiliary speed pattern will not be effective. Thus, this arrangement if used with a low inertia, fast acting car speed sensor switch as a backup, such as the speed sensor disclosed in U.S. Pat. No. 3,814,216, which is assigned to the same assignee as the present application. If the car speed is excessive at the car position relative to the terminal monitored by this speed sensing switch, the car is forced to make an emergency stop.
Application Ser. No. 628,448 filed Nov. 3, 1975, which application is assigned to the same assignee as the present application, discloses a discrete car speed monitoring system, as opposed to the continuous car speed monitoring system of U.S. Pat. No. 3,779,346. This discrete monitoring system monitors car speed as a function of car position at a plurality of discrete speed checkpoints in the hoistway. The car speed is compared with two reference speeds at most car position checkpoints. If the car speed exceeds the lower but not the upper reference speed, the system attempts to decelerate the car by employing an auxiliary terminal slowdown velocity pattern. If the car speed exceeds the upper reference speed at any checkpoint, the car is forced to make an emergency stop.
The present invention is directed to an improvement in elevator car speed monitoring systems which monitor car speed as a function of discrete car positions adjacent to a terminal floor.